The invention relates to a method and an apparatus for the production of binder-bound mineral wool products.
In order to produce upsetting, that is to say longitudinally compressed mineral wool products having an increased fraction of mineral fibres oriented in the direction of thickness of the web, it is customary by mechanical action to reorientate the relative positions of the mineral fibres of a mineral wool web deposited on a production surface, for which purpose the web is guided on its large faces and at the same time upsetting forces are introduced into the web in parallel with the large faces. As compared with the production of lamellar mats or lamellar boards from cut-off lamellae rotated through 90xc2x0, this affords the advantage of the efficient continuous production of mineral wool products with high strength against pressure exerted under large faces of the product.
The introduction of compressive forces into the still uncured mineral fibre web often leads to a reorientation of interconnecting fibre regions with the effect of the formation of creases in the product. Although this is not harmful in terms of pressure resistance, it results in low flexural resistance of a board of this type, since even low tensile forces at the surface cause adjacent creases to gape open. Moreover, the acoustic and thermal insulating properties of such a board decrease considerably in its direction of thickness through the fibre zones lying in the direction of thickness.
In order to avoid these disadvantages, it is known from WO 91/14816 not to apply the longitudinal forces for upsetting along a line which lies transversely to the production direction and in front of which the material is upset and forms creases, but, instead, in discrete introduction zones which lie next to one another in the transverse direction of the web and one behind the other in the direction of run of the web, in each case at a distance from one another, the introduction zones adjacent to one another in the transverse direction being arranged so as to be offset relative to one another in the web running direction. As a result, a sudden linear introduction of the longitudinal forces are exerted as it were in a staggered manner in adjacent width zones of the web. Overall, controlled and finely structured reorientation of the fibres and corresponding product homogeneity, without creases being formed over a large area, are to be achieved thereby.
In this case, the upsetting forces are introduced in the usual way by means of rollers which, however, have relatively small width, a relatively large number of rollers being combined on a common shaft arranged transversely to the web running direction. Shafts adjacent to one another in the running direction rotate at a correspondingly different rotational speed, and shafts with the same roller arrangement, that is to say the rollers of which are in alignment, are moved apart from one another to an extent such that a shaft with corresponding rollers, which, however, are offset in a staggered manner, may be arranged between them. This ensures teat discrete introduction zones are arranged so as to be offset relative to one another over the width of the web.
The introduction zone of each roller on the large face of the web is essentially linear, so that, according to the roller diameter, what is obtained is a distance which is a multiple greater, as compared with the length, measured in the running direction, of the introduction zone of each roller, not only in relation to the rollers located behind it in the direction of alignment, but also in relation to the rollers arranged in between so as to be offset thereto. As a result of the holding-together forces in the composite fibre structure, this narrow linear introduction also results in each roller having a region of action which is greater than the actual contact region, so that these regions of action can overlap one another and lead to a corresponding warping of fibres in the longitudinal and also the transverse direction of the web, thereby counteracting a tendency towards the formation of creases over a large area. These warping forces between the narrow introduction lines lying at a wide distance from one another are nevertheless low; if the acting forces are high, there is the risk that material in the gusset between the rollers will arch upwards and therefore that local distortions and crease formations will occur.
By contrast, the object on which the invention is based is to provide a method and an apparatus, by means of which such high longitudinal forces can be introduced into the web that the material of the mineral wool web is exposed to a fulling action, if appropriate with the fibres simultaneously being upset, warped and felted, so that, if desired, a thin high-density board with correspondingly small air interspaces can be produced.
This object is achieved by means of the present invention.
Consequently, a result of an entirely different quality from that in the generic prior art can be achieved: not primarily reorientation of the fibres such that a large fraction of fibres is aligned in the direction of thickness in the manner of a lamellar or upset board, in order to increase the pressure resistance of the board, but, instead, the fibres are to be intensively felted with one another and warped and also pressed against one another. At the same time, previously horizontal fibres or fibre fragments will also assume a vertical position and thus make a contribution to improving the pressure resistance, but the fulling action occurring in the overlap region of the zones of action leads primarily to felting and compacting reorientation of the fibres or fibre fragments and thus to the consolidation and improvement of the mechanical properties. It is thus possible, if required, to produce a thin board resembling firm cardboard which is resistant to tensile, flexural and upsetting loads in the plane of its large face, that is to say, while having considerable stiffness, neither tears nor easily kinks or bulges, and which, furthermore, because of its small thickness, even without a high fraction of fibres standing vertically, is itself sufficiently pressure-resistant and, after the curing of the binder, has no resilience.
This is achieved by an overlap of introduction zones for the longitudinal forces which are elongated in a sheet-like manner in the longitudinal direction of the web and are arranged so as to be offset next to one another. This overlap region is as it were a departure from the concept of the staggered action of the introduction zones to avoid the formation of creases over a large area and is a return to an active front extending over the entire web width. However, the material, when it impinges on to this active front, is not essentially unguided, contrary to conventional upsetting installations, but, instead, is even guided and held in a virtually sheet-like manner by the trailing introduction zones located next to one another, so that warpings or even crease formations in entire composite fibre structures are nevertheless ruled out. At all events, with small product thicknesses, it is not primarily upsetting of the entering material which takes place in the overlap region, but, instead, horizontal fulling, warping and felting of the material, at the same time with the latter being upset. At the exit of the overlap region, the action of the leading introduction zones ceases, and the material is once again guided cleanly at the introduction zones of the second stage, the felting, warping and compression state achieved in the first overlap region being as it were frozen in and thus being fed, if appropriate, to a second overlap region which has following introduction zones and in which corresponding supplementary further treatment takes place.
In this way, the material can be felted, warped, compressed and fulled as intensively as desired by linking one behind the other a suitable number of introduction zones or rotary members corresponding to overlap regions, the set of introduction zones which in each case follow behind the overlap region maintaining the acquired state until curing commences and fixes this state definitively.
In principle, it is also possible, according to the invention, to treat boards of greater thickness, in order to achieve corresponding fulling, compression and upsetting effects. Where greater product thicknesses are concerned, the effect of acting on the surface in the overlap regions naturally decreases towards the middle of the product. In this middle region, therefore, primarily the upsetting effects increase, but, here too, the formation of creases in entire composite fibre structures over a large area is minimized because longitudinal forces are introduced
differently over the width and, at all events, cannot encroach upon that region of the product surface where, even in the case of large product thicknesses, the felting and compacting effects described occur as a result of the mutual warping and fulling of the fibres, so that a surface capable of being subjected to tensile load, along with a correspondingly high flexural resistance in the product, is obtained.
It is particularly preferred, however, if the smallest height of the upsetting channel is smaller than 40 mm, in particular smaller than 25 mm, so as to thus to produce a cardboard-like thin board. In the case of such a thin board or skin, the depth of the zones of action on the mutually opposite large faces of the board reach as far as the opposite large face of the board, so that essentially homogeneous fulling and felting can be achieved. By contrast, in the case of considerably larger board thicknesses, the effects of the introduction zones decrease towards the middle of the board, since fibre regions in the vicinity of the middle of the board are exposed only to a smaller extent to the actions according to the invention, thus yielding a product still specific to the invention and having a so-called xe2x80x9chard skinxe2x80x9d on the large surfaces thereof.
A mineral wool board according to the invention may be distinguished by a wavy structure of the fibre alignment on the large faces, such as has occurred due to the fulling or shearing action on adjacent introduction zones in the overlap region. If the board thickness is correspondingly small, this wavy structure may often also be seen even inside the board in sections parallel to the large faces. This wavy structure may also be apparent on the narrow sides.
A mineral wool board produced according to the invention is particularly suitable as an outer skin in a composite mineral wool product according to claim 4, specifically irrespective of the type of treatment of the core or of the main layer of this composite product. If the latter is upset in the usual way, with creases being formed, this outer skin generates corresponding tensile strength in this surface and therefore, overall, high flexural resistance in the board. At all events, in the same way as a hard cardboard layer, the outer skin results in effective surface refinement of the composite product and, for example, gives gripping felt sufficient gripping force as a result of the high upsetting resistance of the said outer skin, makes it possible, on account of its tensile strength, for roof insulating boards to have a walk-on capacity, by virtue of its flexural resistance avoids a visual mattress effect on facade insulating boards and, in the case of industrial ceiling boards, any dishing, and, where plaster base boards are concerned, forms an ideal plaster base layer with ideal evenness. Many of these effects can be achieved even when the hard skin is inside the product as it can be obtained by superposing of a plurality of layer with the hard skin in between.